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SHIP FRACTURE

Design of ships against fracture requires, at the simplest level, that the minimum service temperature of the ship coincide with the upper shelf of the structural ductile to brittle transition curve for the steel and weldments. Material specifications in shipping standards often have no requirement for notch toughness and when they do specify toughness the specimen is of insufficient size and notch acuity to reflect the structural transition behaviour and to guarantee that the structure will be ductile at the lowest service temperatures. The Canadian Navy requirement of a minimum Charpy energy of 40 joules at -40C will be put in perspective to other standards and ship losses. In this paper, it will be shown that the transition behaviour for Charpy sized specimens can be 50 to 100C below that for larger Dynamic Tear specimens. It will be shown that replacing the standard notch with an EDM notch in Charpy specimens moves the transition curve towards the Dynamic Tear curve but as little as 20 degrees for some materials. This leaves the Dynamic Tear specimen as the simplest existing specimen whose transition behaviour would approximate that of a structure. Data will be presented for 350WT and A517 steels. Relying on a shear lip width transition curve as opposed to an energy based transition curve in dynamic tear testing cna reduce the cost of testing considerably. TRUNCATED